2D seismic data shows that the Phrae Basin contains three main genetic sequences. There are rift fill, rift fill associated with inversion and post-rift sequences. The rift fill sequence can be separated into early rift fill which occurs locally in the central area and the main rift fill that was deposited throughout the basin. The rift fill associated with inversion is seen into two stages. The first stage is represented by folding in the Rong Kwang sub-basin and in the Phrae sub-basin is expressed by folds and reversal of the eastern fault margin. The second stage is represented by a broad anticline in the rift fill sequence, continued reversal of the eastern border fault and reverse movement on the fault in the centre of the basin. The post-rift sequence covers almost all the basin, except in the central and eastern parts where this unit was uplifted.